Method and apparatus for transmitting and receiving uplink signals in a wireless communication system

ABSTRACT

A method for allowing a user equipment (UE) and a base station (BS) to transmit and receive uplink (UL) signals in a wireless communication system is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application under 35 U.S.C. § 371of International Application No. PCT/KR2018/007154, filed on Jun. 25,2018, which claims the benefit of U.S. Provisional Application No.62/523,785, filed on Jun. 23, 2017. The disclosures of the priorapplications are incorporated by reference in their entirety.

TECHNICAL FIELD

The following description relates to a wireless communication system,and more particularly to a method and apparatus for transmitting andreceiving an uplink signal.

Background Art

As many more communication devices have required higher communicationcapacity, the necessity of the enhanced mobile broadband (eMBB)communication much improved than the legacy radio access technology(RAT) has increased. In addition, massive machine type communication(mMTC) capable of providing various services at anytime and anywhere byconnecting a number of devices or objects to each other has beenconsidered in the next generation communication system.

Moreover, a communication system design capable of supportingservices/UEs sensitive to reliability and latency has been discussed.The introduction of the next generation RAT considering the eMBBcommunication, mMTC, Ultra-reliable and low latency communication(URLLC), and the like has been discussed.

DISCLOSURE Technical Problem

An object of the present disclosure devised to solve the problem lies ina method for more efficiently adjusting uplink synchronization in awireless communication system.

In particular, it is another object of the present disclosure to providea method for more efficiently determining a timing advance (TA) value ina wireless communication system.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

Technical Solutions

In accordance with one aspect of the present disclosure, a method fortransmitting an uplink signal by a user equipment (UE) in a wirelesscommunication system includes receiving a random access response (RAR)message including a first timing advance (TA) command, determining afirst timing advance (TA) value for transmitting a first uplink signalbased on the first TA command and a subcarrier spacing of an uplinkchannel to be initially transmitted after reception of the random accessresponse (RAR) message, and transmitting the first uplink signalaccording to the first TA value.

An exemplary embodiment of the method may further include receiving adownlink channel including a second timing advance (TA) command,determining a second TA value for transmitting a second uplink signalbased on the second TA command, and transmitting the second uplinksignal according to the second TA value, and if the UE has a pluralityof uplink bandwidth parts, the second TA value is determined based on alargest value among subcarrier spacing values of the plurality of uplinkbandwidth parts and the second command.

In an exemplary embodiment of the method, when the second uplink signalis transmitted in an uplink bandwidth part which has a subcarrierspacing smaller than a subcarrier spacing used for determining thesecond TA value among the plurality of uplink bandwidth parts, thesecond TA value is determined by rounding-off a value indicated by thesecond TA command based on a basic unit of a TA value.

In accordance with another aspect of the present disclosure, a userequipment (UE) for transmitting an uplink signal in a wirelesscommunication system includes a transceiver and a processor. Theprocessor is configured to control the transceiver to receive a randomaccess response (RAR) message including a first timing advance (TA)command, determine a first timing advance (TA) value for transmitting afirst uplink signal based on the first TA command and a subcarrierspacing of an uplink channel to be initially transmitted after receptionof the random access response (RAR) message, and control the transceiverto transmit the first uplink signal according to the first TA value.

An exemplary embodiment of the processor is further configured tocontrol the transceiver to receive a downlink channel including a secondtiming advance (TA) command, determine a second TA value fortransmitting a second uplink signal based on the second TA command, andtransmit the second uplink signal according to the second TA value. Ifthe UE has a plurality of uplink bandwidth parts, the second TA value isdetermined based on a largest value among subcarrier spacing values ofthe plurality of uplink bandwidth parts and the second TA command.

An exemplary embodiment of the method may further include determining abasic unit of a timing advance (TA) value based on the subcarrierspacing of the uplink channel to be initially transmitted afterreception of the random access response (RAR) message, and the first TAvalue may be determined based on the basic unit of the TA value and thefirst TA command.

The first TA value may be in proportion to a value indicated by thefirst TA command, and may be in inverse proportion to the subcarrierspacing.

Advantageous Effects

As is apparent from the above description, the embodiments of thepresent disclosure may more efficiently adjust uplink (UL)synchronization in a wireless communication system.

The embodiments of the present disclosure may more efficiently determinea timing advance (TA) value in a wireless communication system.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present disclosure are notlimited to what has been particularly described hereinabove and otheradvantages of the present disclosure will be more clearly understoodfrom the following detailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 is a view illustrating physical channels and a general signaltransmission method using the physical channels in a 3GPP system.

FIG. 2 is a view illustrating an exemplary slot structure available innew radio access technology (NR).

FIG. 3 is a view illustrating exemplary connection schemes betweentransceiver units (TXRUs) and antenna elements.

FIG. 4 is a view abstractly illustrating a hybrid beamforming structurein terms of TXRUs and physical antennas.

FIG. 5 is a view illustrating an exemplary cell in an NR system.

FIG. 6 is a conceptual diagram illustrating a method for allowing a userequipment (UE) to transmit an uplink (UL) signal on the basis of atiming advance (TA) value.

FIG. 7 is a conceptual diagram illustrating exemplary methods forapplying a round-off or round-up operation to a TA value that iscalculated on the basis of the number of samples.

FIG. 8 is a flowchart illustrating an uplink (UL) transmission methodaccording to an embodiment of the present disclosure.

FIG. 9 is a diagram illustrating a configuration of a user equipment(UE) and a base station (BS).

BEST MODE

Reference will now be made in detail to the embodiments of the presentdisclosure with reference to the accompanying drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present disclosure, rather than to show the only embodiments thatcan be implemented according to the disclosure.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical spirit andscope of the present disclosure.

The detailed description, which will be given below with reference tothe accompanying drawings, is intended to explain exemplary embodimentsof the present disclosure, rather than to show the only embodiments thatcan be implemented according to the disclosure.

Although the terms used in the present disclosure are selected fromgenerally known and used terms while considering functions of thepresent disclosure, they may vary according to intention or customs ofthose skilled in the art or emergence of new technology. Some of theterms mentioned in the description of the present disclosure may havebeen selected by the applicant at his or her discretion, and in suchcases the detailed meanings thereof will be described in relevant partsof the description herein. Thus, the terms used in this specificationshould be interpreted based on the substantial meanings of the terms andthe whole content of this specification rather than their simple namesor meanings.

The embodiments of the present disclosure described hereinbelow arecombinations of elements and features of the present disclosure. Theelements or features may be considered selective unless mentionedotherwise. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent disclosure may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent disclosure may be rearranged. Some constructions or features ofany one embodiment may be included in another embodiment and may bereplaced with corresponding constructions or features of anotherembodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present disclosure will be avoided lestit should obscure the subject matter of the present disclosure. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

Throughout the specification, when a certain portion “includes” or“comprises” a certain component, this indicates that other componentsare not excluded and may be further included unless otherwise noted. Theterms “unit”, “-or/er” and “module” described in the specificationindicate a unit for processing at least one function or operation, whichmay be implemented by hardware, software or a combination thereof. Inaddition, the terms “a” (or “an”), “one”, “the”, etc. may include asingular representation and a plural representation in the context ofthe present disclosure (more particularly, in the context of thefollowing claims) unless indicated otherwise in the specification orunless context clearly indicates otherwise.

Terms to be used in this application are defined as follows.

In the following description, a user equipment (UE) may be a fixed ormobile user equipment (UE), and may be any one of various devices thattransmit and receive user data and/or various kinds of controlinformation by communicating with a base station (BS). The UE may bereferred to as a Terminal Equipment, Mobile Station (MS), MobileTerminal (MT), User Terminal (UT), Subscriber Station (SS), wirelessdevice, Personal Digital Assistant (PDA), wireless modem, or handhelddevice.

In the following description, a Base Station (BS) is a fixed stationthat generally communicates with a UE or another BS. The BS communicateswith a UE or another BS to exchange various kinds of data and controlinformation with a UE or another BS. The BS may be referred to as anAdvanced Base Station (ABS), Node-B (NB), evolved-NodeB (eNB), BaseTransceiver System (BTS), Access Point (AP), or Processing Server (PS).Specifically, a base station (BS) of UTRAN will hereinafter be referredto as Node-B, a base station (BS) of E-UTRAN will hereinafter bereferred to as eNB, and a base station (BS) of a new radio accesstechnology network will hereinafter be referred to as gNB.

Techniques, devices, and systems described herein can be used in variouswireless multiple access systems such as Code Division Multiple Access(CDMA), Frequency Division Multiple Access (FDMA), Time DivisionMultiple Access (TDMA), Orthogonal Frequency Division Multiple Access(OFDMA), Single Carrier-Frequency Division Multiple Access (SC-FDMA),Multi-Carrier Frequency Division Multiple Access (MC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communication (GSM),General Packet Radio Service (GPRS), and Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asInstitute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi),IEEE 802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunication System (UMTS) and3^(rd) Generation Partnership Project (3GPP) Long Term Evolution (LTE)is a part of Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMAfor downlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE.For the sake of clarity, it is assumed that the present disclosure isapplied to 3GPP communication systems, for example, LTE/LTE-A systems,NR (New Radio Access Technology) system, etc. However, the technicalfeatures of the present disclosure are not limited thereto. For example,while the following detailed description is given under the assumptionthat a 3GPP communication system is being used as a mobile communicationsystem, the description is applicable to any other mobile communicationsystem except for specific features inherent to the 3GPP LTE/LTE-A/NRsystems.

The 3GPP communication standards define downlink (DL) physical channelscorresponding to resource elements (REs) carrying information originatedfrom a higher layer, and DL physical signals which are used in thephysical layer and correspond to REs which do not carry informationoriginated from a higher layer. For example, physical downlink sharedchannel (PDSCH), physical broadcast channel (PBCH), physical multicastchannel (PMCH), physical control format indicator channel (PCFICH),physical downlink control channel (PDCCH), and physical hybrid ARQindicator channel (PHICH) are defined as DL physical channels, andreference signals (RSs) and synchronization signals (SSs) are defined asDL physical signals.

An RS is a signal with a predefined special waveform known to both agNode B (gNB) and a UE, and may also be referred to as a pilot. Forexample, cell specific RS, UE-specific RS (UE-RS), positioning RS (PRS),and channel state information RS (CSI-RS) are defined as DL RSs.

The 3GPP LTE/LTE-A standards define uplink (UL) physical channelscorresponding to REs carrying information originated from a higherlayer, and UL physical signals which are used in the physical layer andcorrespond to REs which do not carry information originated from ahigher layer. For example, physical uplink shared channel (PUSCH),physical uplink control channel (PUCCH), and physical random accesschannel (PRACH) are defined as UL physical channels, and a demodulationreference signal (DMRS) for a UL control/data signal, and a soundingreference signal (SRS) used for UL channel measurement are defined as ULphysical signals.

In the present disclosure, the PDCCH/PCFICH/PHICH/PDSCH refers to a setof time-frequency resources or a set of REs, which carry downlinkcontrol information (DCI)/a control format indicator (CFI)/a DLacknowledgement/negative acknowledgement (ACK/NACK)/DL data. Further,the PUCCH/PUSCH/PRACH refers to a set of time-frequency resources or aset of REs, which carry UL control information (UCI)/UL data/a randomaccess signal.

In the present disclosure, if it is said that a UE transmits aPUCCH/PUSCH/PRACH, this means that UCI/UL data/a random access signal istransmitted on or through the PUCCH/PUSCH/PRACH. Further, if it is saidthat a gNB transmits a PDCCH/PCFICH/PHICH/PDSCH, this means thatDCI/control information is transmitted on or through thePDCCH/PCFICH/PHICH/PDSCH.

For the terms and techniques which are used herein but not specificallydescribed, 3GPP LTE/LTE-A standard documents, for example, 3GPP TS36.211, 3GPP TS 36.212, 3GPP TS 36.213, 3GPP TS 36.321 and 3GPP TS36.331 may be referenced, and 3GPP NR standard documents, for example,3GPP TS 38.211, 3GPP TS 38.212, 3GPP 38.213, 3GPP 38.214, 3GPP 38.215,3GPP TS 38.321 and 3GPP TS 38.331 may also be referenced.

FIG. 1 illustrates physical channels and a general method fortransmitting signals on the physical channels in the 3GPP system.

Referring to FIG. 1, when a UE is powered on or enters a new cell, theUE performs initial cell search (S201). The initial cell search involvesacquisition of synchronization to an eNB. Specifically, the UEsynchronizes its timing to the eNB and acquires a cell identifier (ID)and other information by receiving a primary synchronization channel(P-SCH) and a secondary synchronization channel (S-SCH) from the eNB.Then the UE may acquire information broadcast in the cell by receiving aphysical broadcast channel (PBCH) from the eNB. During the initial cellsearch, the UE may monitor a DL channel state by receiving a DownLinkreference signal (DL RS).

After the initial cell search, the UE may acquire detailed systeminformation by receiving a physical downlink control channel (PDCCH) andreceiving a physical downlink shared channel (PDSCH) based oninformation included in the PDCCH (S202).

If the UE initially accesses the eNB or has no radio resources forsignal transmission to the eNB, the UE may perform a random accessprocedure with the eNB (S203 to S206). In the random access procedure,the UE may transmit a predetermined sequence as a preamble on a physicalrandom access channel (PRACH) (S203 and S205) and may receive a responsemessage to the preamble on a PDCCH and a PDSCH associated with the PDCCH(S204 and S206). In the case of a contention-based RACH, the UE mayadditionally perform a contention resolution procedure.

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S207) and transmit a physical uplink shared channel(PUSCH) and/or a physical uplink control channel (PUCCH) to the eNB(S208), which is a general DL and UL signal transmission procedure.Particularly, the UE receives downlink control information (DCI) on aPDCCH. Herein, the DCI includes control information such as resourceallocation information for the UE. Different DCI formats are definedaccording to different usages of DCI.

Control information that the UE transmits to the eNB on the UL orreceives from the eNB on the DL includes a DL/UL acknowledgment/negativeacknowledgment (ACK/NACK) signal, a channel quality indicator (CQI), aprecoding matrix index (PMI), a rank indicator (RI), etc. In the 3GPPLTE system, the UE may transmit control information such as a CQI, aPMI, an RI, etc. on a PUSCH and/or a PUCCH.

As a number of communication devices have required higher communicationcapacity, the necessity of the mobile broadband communication muchimproved than the existing radio access technology (RAT) has increased.In addition, massive machine type communications (MTC) capable ofproviding various services at anytime and anywhere by connecting anumber of devices or things to each other has been considered in thenext generation communication system. Moreover, a communication systemdesign capable of supporting services/UEs sensitive to reliability andlatency has been discussed. As described above, the introduction of thenext generation RAT considering the enhanced mobile broadbandcommunication, massive MTC, Ultra-reliable and low latency communication(URLLC), and the like has been discussed.

In the current 3GPP, many developers and companies are conductingintensive research into the next generation mobile communication systemafter EPC. The next generation mobile communication system after EPC maybe referred to as a new RAT (NR) system, a 5G RAT system, or a 5Gsystem. For convenience of description, the next generation mobilecommunication system after EPC will hereinafter be referred to as an NRsystem.

Higher and superior performances better than those of the legacy 4Gsystem in terms of a data rate, capacity, latency, energy consumption,and energy costs should be supplied to the NR system. Therefore, it isnecessary for the NR system to be significantly evolved in variousfields, i.e., a bandwidth, spectral, energy, signaling efficiency, andcost-per-bit reduction.

The NR system may use the OFDM transmission scheme or other similartransmission methods. For example, the NR system may use numerologiesshown in the following Table 1.

TABLE 1 Parameter Value Subcarrier-spacing (Δf) 60 kHz OFDM symbollength 16.33 us Cyclic Prefix (CP) length 1.30 us/1.17 us System BW 80MHz No. of available subcarriers 1200 Subframe length 0.25 ms Number ofOFDM symbol per Subframe 14 symbol

The NR system may be based on OFDM parameters of the LTE system andother parameters. Alternatively, the NR system may be based onnumerologies of the legacy LTE/LTE-A without change, and may have alarger system bandwidth (e.g., 100 MHz) as compared to the legacyLTE/LTE-A. In addition, the NR system may allow one cell to support aplurality of numerologies. That is, in the NR system, UEs operating indifferent numerologies may coexist in one cell.

In the 3GPP LTE/LTE-A system, a radio frame is 10 ms (307200 Ts) long,including 10 equal-size subframes (SFs). The 10 SFs of one radio framemay be assigned numbers. Ts represents a sampling time and is expressedas Ts=1/(2048*15 kHz). Each SF is 1 ms, including two slots. The 20slots of one radio frame may be sequentially numbered from 0 to 19. Eachslot has a length of 0.5 ms. A time taken to transmit one SF is definedas a transmission time interval (TTI). A time resource may bedistinguished by a radio frame number (or radio frame index), an SFnumber (or SF index), a slot number (or slot index), and so on. A TTIrefers to an interval in which data may be scheduled. In the currentLTE/LTE-A system, for example, there is a UL grant or DL granttransmission opportunity every 1 ms, without a plurality of UL/DL grantopportunities for a shorter time than 1 ms. Accordingly, a TTI is 1 msin the legacy LTE/LTE-A system.

FIG. 2 illustrates an exemplary slot structure available in the newradio access technology (NR).

To minimize a data transmission delay, a slot structure in which acontrol channel and a data channel are multiplexed in time divisionmultiplexing (TDM) is considered in NR system.

In FIG. 2, an area marked with slanted lines represents a transmissionregion of a DL control channel (e.g., PDCCH) carrying DCI, and a blackpart represents a transmission region of a UL control channel (e.g.,PUCCH) carrying UCI. DCI is control information which is transmittedfrom a gNB to a UE, and may include information about a cellconfiguration that a UE should know, DL-specific information such as DLscheduling, and UL-specific information such as a UL grant. Further, UCIis control information which is transmitted from a UE to a gNB. The UCImay include an HARQ ACK/NACK report for DL data, a CSI report for a DLchannel state, a scheduling request (SR), and so on.

In FIG. 2, symbols with symbol index 1 to symbol index 12 may be usedfor transmission of a physical channel (e.g., PDSCH) carrying DL data,and also for transmission of a physical channel (e.g., PUSCH) carryingUL data. Referring to FIG. 2, DL transmission and UL transmission takeplace sequentially in one slot, and transmission/reception of DL dataand reception/transmission of a UL ACK/NACK for the DL data may beperformed in the one slot. Therefore, when an error is generated duringdata transmission, a time taken for a data retransmission may bereduced, thereby minimizing the delay of a final data transmission.

In slot structure illustrated in FIG. 2, a time gap is required to allowa gNB and a UE to switch from a transmission mode to a reception mode orfrom the reception mode to the transmission mode. For the switchingbetween the transmission mode and the reception mode, some OFDM symbolcorresponding to a DL-to-UL switching time is configured as a guardperiod (GP) in the slot structure.

In the NR system, a basic transmission unit is a slot. A slot durationincludes 14 symbols each having a normal cyclic prefix (CP), or 12symbols each having an extended CP. In addition, a slot is scaled intime by a function of a used subcarrier spacing.

For an NR system under discussion, a technique of using an ultra-highfrequency band (for example, a frequency band at or above 6 GHz) isconsidered in order to transmit data to a plurality of users at a hightransmission rate in a wide frequency band. However, the ultra-highfrequency band has the frequency property that a signal is attenuatedtoo rapidly according to a distance due to the use of too high afrequency band. Accordingly, the NR system using a frequency band at orabove at least 6 GHz employs a narrow beam transmission scheme in whicha signal is transmitted with concentrated energy in a specificdirection, not omni-directionally, to thereby compensate for the rapidpropagation attenuation and thus overcome the decrease of coveragecaused by the rapid propagation attenuation. However, if a service isprovided by using only one narrow beam, the service coverage of one gNBbecomes narrow, and thus the gNB provides a service in a wideband bycollecting a plurality of narrow beams.

As a wavelength becomes short in the millimeter frequency band, that is,millimeter wave (mmW) band, it is possible to install a plurality ofantenna elements in the same area. For example, a total of 100 antennaelements may be installed at (wavelength) intervals of 0.5 lamda in a30-GHz band with a wavelength of about 1 cm in a two-dimensional (2D)array on a 5 by 5 cm panel. Therefore, it is considered to increasecoverage or throughput by increasing a beamforming gain through use of aplurality of antenna elements in mmW.

To form a narrow beam in the millimeter frequency band, a beamformingscheme is mainly considered, in which a gNB or a UE transmits the samesignals with appropriate phase differences through multiple antennas, tothereby increase energy only in a specific direction. Such beamformingschemes include digital beamforming for generating a phase differencebetween digital baseband signals, analog beamforming for generating aphase difference between modulated analog signals by using a time delay(i.e., a cyclic shift), and hybrid beamforming using both digitalbeamforming and analog beamforming. If a TXRU is provided per antennaelement to enable control of transmission power and a phase per antenna,independent beamforming per frequency resource is possible. However,installation of TXRUs for all of about 100 antenna elements is noteffective in terms of cost. That is, to compensate for rapid propagationattenuation in the millimeter frequency band, multiple antennas shouldbe used, and digital beamforming requires as many RF components (e.g.,digital to analog converters (DACs), mixers, power amplifiers, andlinear amplifiers) as the number of antennas. Accordingly,implementation of digital beamforming in the millimeter frequency bandfaces the problem of increased cost of communication devices. Therefore,in the case where a large number of antennas are required as in themillimeter frequency band, analog beamforming or hybrid beamforming isconsidered. In analog beamforming, a plurality of antenna elements aremapped to one TXRU, and the direction of a beam is controlled by ananalog phase shifter. A shortcoming with this analog beamforming schemeis that frequency selective beamforming (BF) cannot be provided becauseonly one beam direction can be produced in a total band. Hybrid BFstands between digital BF and analog BF, in which B TXRUs fewer than Qantenna elements are used. In hybrid BF, the directions of beamstransmittable at the same time are limited to or below B although thenumber of beam directions is different according to connections betweenB TXRUs and Q antenna elements.

FIG. 3 is a view illustrating exemplary connection schemes between TXRUsand antenna elements.

(a) of FIG. 3 illustrates connection between a TXRU and a sub-array. Inthis case, an antenna element is connected only to one TXRU. Incontrast, (b) of FIG. 5 illustrates connection between a TXRU and allantenna elements. In this case, an antenna element is connected to allTXRUs. In FIG. 5, W represents a phase vector subjected tomultiplication in an analog phase shifter. That is, a direction ofanalog beamforming is determined by W. Herein, CSI-RS antenna ports maybe mapped to TXRUs in a one-to-one or one-to-many correspondence.

As mentioned before, since a digital baseband signal to be transmittedor a received digital baseband signal is subjected to a signal processin digital beamforming, a signal may be transmitted or received in orfrom a plurality of directions on multiple beams. In contrast, in analogbeamforming, an analog signal to be transmitted or a received analogsignal is subjected to beamforming in a modulated state. Thus, signalscannot be transmitted or received simultaneously in or from a pluralityof directions beyond the coverage of one beam. A gNB generallycommunicates with multiple users at the same time, relying on thewideband transmission or multiple antenna property. If the gNB usesanalog BF or hybrid BF and forms an analog beam in one beam direction,the gNB has no way other than to communicate only with users covered inthe same analog beam direction in view of the nature of analog BF. Alater-described RACH resource allocation and gNB resource utilizationscheme according to the present disclosure is proposed by reflectinglimitations caused by the nature of analog BF or hybrid BF.

FIG. 4 abstractly illustrates a hybrid beamforming structure in terms ofTXRUs and physical antennas.

For the case where multiple antennas are used, hybrid BF with digital BFand analog BF in combination has emerged. Analog BF (or RF BF) is anoperation of performing precoding (or combining) in an RF unit. Due toprecoding (combining) in each of a baseband unit and an RF unit, hybridBF offers the benefit of performance close to the performance of digitalBF, while reducing the number of RF chains and the number of DACs (oranalog to digital converters (ADCs). For the convenience sake, a hybridBF structure may be represented by N TXRUs and M physical antennas.Digital BF for L data layers to be transmitted by a transmission end maybe represented as an N-by-N matrix, and then N converted digital signalsare converted to analog signals through TXRUs and subjected to analog BFrepresented as an M-by-N matrix.

In FIG. 4, the number of digital beams is L, and the number of analogbeams is N. Further, it is considered in the NR system that a gNB isconfigured to change analog BF on a symbol basis so as to moreefficiently support BF for a UE located in a specific area. Further,when one antenna panel is defined by N TXRUs and M RF antennas,introduction of a plurality of antenna panels to which independenthybrid BF is applicable is also considered.

In the case where a gNB uses a plurality of analog beams, a differentanalog beam may be preferred for signal reception at each UE. Therefore,a beam sweeping operation is under consideration, in which for at leastan SS, system information, and paging, a gNB changes a plurality ofanalog beams on a symbol basis in a specific slot or SF to allow all UEsto have reception opportunities.

FIG. 5 is a view illustrating an exemplary cell in the NR system.

Referring to FIG. 5, compared to a wireless communication system such aslegacy LTE in which one eNB forms one cell, configuration of one cell bya plurality of TRPs is under discussion in the NR system. If a pluralityof TRPs form one cell, even though a TRP serving a UE is changed,seamless communication is advantageously possible, thereby facilitatingmobility management for UEs.

Compared to the LTE/LTE-A system in which a PSS/SSS is transmittedomni-directionally, a method for transmitting a signal such as aPSS/SSS/PBCH through BF performed by sequentially switching a beamdirection to all directions at a gNB applying mmWave is considered. Thesignal transmission/reception performed by switching a beam direction isreferred to as beam sweeping or beam scanning. In the presentdisclosure, “beam sweeping” is a behavior of a transmission side, and“beam scanning” is a behavior of a reception side. For example, if up toN beam directions are available to the gNB, the gNB transmits a signalsuch as a PSS/SSS/PBCH in the N beam directions. That is, the gNBtransmits an SS such as the PSS/SSS/PBCH in each direction by sweeping abeam in directions available to or supported by the gNB. Or if the gNBis capable of forming N beams, the beams may be grouped, and thePSS/SSS/PBCH may be transmitted/received on a group basis. One beamgroup includes one or more beams. Signals such as the PSS/SSS/PBCHtransmitted in the same direction may be defined as one SS block (SSB),and a plurality of SSBs may exist in one cell. If a plurality of SSBsexist, an SSB index may be used to identify each SSB. For example, ifthe PSS/SSS/PBCH is transmitted in 10 beam directions in one system, thePSS/SSS/PBCH transmitted in the same direction may form an SSB, and itmay be understood that 10 SSBs exist in the system.

FIG. 6 is a conceptual diagram illustrating a method for allowing a userequipment (UE) to transmit an uplink (UL) signal on the basis of atiming advance (TA) value.

The mobile communication system should provide services to a pluralityof UEs in a single frequency band, such that various methods foridentifying the UEs from one another are needed. Specifically,differently from downlink through which signals of all UEs can betransmitted by synchronizing with the same reference time, UEs for usein uplink are unable to have the same reference time such that a methodfor multiplexing the UEs on uplink is needed.

In the case of using CDMA communication such as in the 3G system, a basestation (BS) may be designed to identify different UEs using differentcodes. A base station (BS) for use in the 4G system may be designed toidentify different UEs by independently allocating resources on afrequency axis or a time axis. In this case, in order to allow the BS todynamically schedule resources on the time axis, a plurality of UEs mustadjust an arrival time of an uplink (UL) signal on the basis of a signalreception time at which the UEs have received signals from the BS.

In order to maintain UL time synchronization, the BS may transmit a timeadvance (TA) value to each UE, and the UE may advance or delay atransmission (Tx) time point based on the TA value received from the BS.The BS may calculate the TA value of the UE using various methods, andmay transmit the calculated TA value to the UE. In this case, the TAvalue may be transmitted through a Timing Advance Command (TAC), and theTA command may refer to information indicating the TA value. The TAcommand may be transmitted through a random access response (RAR), ormay be periodically transmitted through a Medium Access Control (MAC)Control Element (CE). The UE of the idle mode may receive the TA commandthrough RAR, and a UE of a connected mode may receive the TA commandthrough RAR or MAC CE. One case in which the UE receives the TA commandthrough RAR and the other case in which the UE receives the TA commandthrough MAC CE will hereinafter be described in detail.

For example, if the UE receives the TA command through RAR and transmitsa random access preamble to the BS, the BS may calculate the TA value onthe basis of the random access preamble received from the UE. The BS maytransmit a random access response (RAR) including the calculated TAvalue to the UE, and may update an UL Tx time point using the receivedTA value.

The random access response (RAR) may include a TA command, a UL grant,and a temporary C-RNTI.

The UL grant may include uplink resource allocation information and atransmit power command (TPC) for use in transmission of a schedulingmessage. TPC may be used to decide Tx power for the scheduled PUSCH. TheUE may transmit a scheduled message to the BS according to the UL grantcontained in the random access response (RAR). In accordance with oneembodiment, a random access preamble, a random access response (RAR)message, and a scheduled message may be referred to as ‘M1 message’, ‘M2message’, and ‘M3 message’, respectively. ‘M1 message’, ‘M2 message’,and ‘M3 message’ may also be referred to as ‘Message 1 (Msg1)’, ‘Message2 (Msg2)’, and ‘Message 3 (Msg3)’, respectively.

In addition, when the UE receives the TA command through MAC CE, the BSmay periodically or arbitrarily receive a sounding reference signal(SRS) from the UE, and may calculate the TA value of the UE on the basisof the received SRS. The BS may inform the UE of the calculated TA valuethrough the MAC CE. In this case, a periodic TA command transmittedthrough MAC CE may include a value that is updated on the basis of theprevious TA value. For example, assuming that the previous TA value is‘100 Ts’ and a TA value indicated by the TA command that has beentransmitted through the MAC CE is ‘−16 Ts’, the UE may determine ‘84 Ts(100 Ts−16 Ts)’ to be a TA value for UL signal transmission. The UE maytransmit the UL signal on the basis of 84 Ts.

Therefore, in the LTE system, the BS may transmit the TA value to theUE, and the UE may advance a scheduled time by the TA value receivedfrom the BS and then transmit the UL signal at the advanced time.

Referring to FIG. 6, UEs may be synchronized in time with the BS using areference signal (e.g., a synchronization signal and a CRS for use inthe LTE system) that is transmitted on downlink. In this case, thesynchronization time at which each UE is synchronized with the BS may bedifferent from the actual BS time by a predetermined time. For example,the synchronization time at which each UE is synchronized with the BSmay be different from the actual BS time by a propagation delay, and thepropagation delay may refer to a delay time to be consumed for radiowaves moving by a distance between the BS and the UEs. Therefore, if UEstransmit the UL signal with respect to the time synchronized with the BSon downlink, a time difference may occur in a duration time during whichthe UL signal is transferred from each UE to the BS, according to therespective UEs that have transmitted the UL signal. In this case,according to the respective UEs having transmitted the UL signal, a timedifference corresponding to a round-trip delay time between the BS andeach UE may occur. Therefore, the BS may transmit the TA value to the UEthrough the TA command in a manner that the UE can transmit the ULsignal at an earlier time advanced by the round-trip delay between theBS and the UE.

The TA command may be transmitted through a response message (e.g., arandom access response (RAR) message) about the RACH signal transmittedin an initial access process. In the connected mode after completion ofthe initial access process, the TA command may be periodicallytransmitted to the UE on the basis of either the SRS received from theUE or a specific value measured through PUSCH/PUCCH.

Generally, if non-transmission or non-reception of the TA commandoccurs, the UE position may be changed over time such that there is atime difference between UL signal reception time points and the UE mayenter the out-of-sync state on uplink. Therefore, if the UE does notreceive the TA command for a given time, the UE may performre-connection to the BS.

The UE generally has mobility, such that the signal Tx time point of theUE may be changed according to movement speed and position of the UE.Therefore, the TA value transferred from the BS to the UE may be validfor a specific time. In order to allow the TA value to be valid for thespecific time, a Time Alignment Timer (TAT) may be used.

For example, if the UE receives the TA value from the BS and updatestime synchronization (or time alignment), the UE may initiate the timealignment timer (TAT) or may restart the TAT. The UE may transmit the ULsignal only during operation of the TAT. The TAT value may betransmitted from the BS to the UE through system information or a radioresource control (RRC) message such as a radio bearer reconfiguration(RBR) message.

If the TAT has expired or if the TAT does not operate any more, the UEmay determine that time synchronization with the BS is incorrect, suchthat the UE may not transmit any UL signals other than the random accesspreamble.

In the LTE system, in order to apply an independent TA to each servingcell, a TA group (TAG) may be defined. The TA group (TAG) may includeone or more cells to which the same TA is applied. TA may be applied toeach TA group, and the time alignment timer may also operate for each TAgroup.

The TA command for the TA group may indicate an uplink timing changeabout a current UL timing for each TA group using a multiple of 16 Ts.In the case of random access response (RAR), 11-bit TA command (T_(A))for the TA group may indicate a value of N_(TA) using an index value ofT_(A). If a UE is configured in a secondary cell group (SCG), the T_(A)index value may be any of 0, 1, 2, . . . , 256. If the UE is configuredin a primary cell group (PCG), the T_(A) index value may be any of 0, 1,2, . . . , 1282. In this case, the TA value for the TA group may begiven as ‘N_(TA)=16TA’.

In accordance with another embodiment, a 6-bit TA command for the TAgroup may indicate that, for the T_(A) index value, a current N_(TA)value (N_(TA,old)) is adjusted using a new N_(TA) value (N_(TA,new)). Inthis case, the T_(A) value may be any of 0, 1, 2, . . . , 63, andN_(TA,new)

may be denoted by ‘N_(TA,old)+(T_(A)−31)×16’. In this case, theoperation for adjusting the N_(TA) value to be a positive (+) number ora negative (−) number may indicate that the UL Tx time point for the TAgroup may be advanced or delayed by a given magnitude.

If the TA command is received on the N-th subframe, adjusting the UL Txtime point corresponding to the received TA may be applied to subframesstarting from the (N+6)-th subframe. In association with the servingcells of the same TA group, if UL transmission (e.g., PUCCH/PUSCH/SRS)of the UE at the N-th subframe and UL transmission (e.g.,PUCCH/PUSCH/SRS) of the UE at the (N+1)-th subframe are overlapped witheach other due to time adjustment, the UE may finish transmission of theN-th subframe and may not transmit the overlapped part between the N-thsubframe and the (N+1)-th subframe.

If the received DL time point is changed, and if the changed DL timepoint is not compensated or is partially compensated by UL timingadjustment without using the TA command, the UE may change the N_(TA)value according to the changed DL time point.

In addition, although various system bandwidths ranging from 1.4 MHz to20 MHz are defined in the LTE system, a single numerology of 15 kHz(hereinafter the term “numerology” may refer to subcarrier spacing) maybe defined in the subcarrier spacing (SCS). In addition, the cyclicprefix (CP) length may be defined based on the 15 kHz subcarrierspacing, and may be equally defined in all system bandwidths.

The UE may basically support all system bandwidths, and the samplingfrequency may be set to any of 1.92˜30.72 MHz according to systembandwidths. Under the environment in which various system bandwidth aredefined, the UE does not recognize the BS system bandwidth in theinitial access process, such that the UE may attempt to access the BS onthe basis of either a minimum bandwidth defined in a frequency bandcurrently connected to the UE or a minimum bandwidth supported by theLTE system. In this case, the UE may operate a transceiver (or a Tx/Rxmodule or a communication module) using the sample frequency of 1.92MHz, such that it is preferable that the TA command transmitted by theBS be applied in units of 16 T_(s). In this case, T_(s) is 1/30.72 MHz,and may correspond to a minimum sampling time defined by the LTE system.That is, 16 T_(s) may refer to the sampling time corresponding to thesampling frequency 1.92 MHz. Therefore, in order for the LTE system toallow TA-associated resolution in the initial access to be identical toTA-associated resolution in the connected mode, a basic unit of the TAvalue may be defined as 16 T_(s). In this case, the CP length is about 5usec, and the same CP length is used in all system bandwidth. Therefore,an unexpected error corresponding to about 1/18 CP length may occur intime adjustment of UL transmission (UL Tx time adjustment) through TA,irrespective of the system bandwidth.

In the NR system, it is expected that a basic initial access process anda UL Tx time adjustment using the TA will be similar to those of the LTEsystem. However, differently from the LTE system, the NR system may usevarious frequency bands ranging from several hundreds of MHz to severaltens of GHz, and may also use different usage cases or different cellenvironments according to individual frequency bands. Therefore, the NRsystem may support various numerologies (e.g., subcarrier spacing of 15,30, 60, 120 or 240 kHz on the basis of a data channel). In addition,various numerologies are supported, such that various CP lengths may bedefined, and the CP length is generally determined in inverse proportionto the subcarrier spacing. In addition, the NR system may allow therespective UEs to use different numerologies according to servicesoperating in a single system bandwidth. If different numerologies areused for the respective UEs, the LTE system operation for interpretingthe TA value transmitted through the TA command on the basis of only onebasic unit may be considered inefficient in terms of signaling overhead.Therefore, the present disclosure may provide a method for configuringthe basic unit of the TA value according to numerologies. In this case,the basic unit of the TA value may be commonly applied to an absolute TAvalue (e.g., a TA value transmitted through a random access response(RAR) message and a TA value transmitted through a TA command in theconnected mode).

1. Method 1: Method for Configuring Basic Unit of TA Value According toSubcarrier Spacing of SS Block

The NR system may support a wider frequency band as compared to the LTEsystem. Therefore, the NR system has a much larger difference infrequency offset according to frequency bands as compared to the LTEsystem, such that the subcarrier spacing of a synchronization signal(SS) block for use in the NR system is defined according to thefrequency bands such that time and frequency synchronization can beefficiently carried out in the NR system using the defined subcarrierspacing of the SS block.

A large subcarrier spacing of the SS block may indicate that a frequencybandwidth of a data channel transmitted in the corresponding frequencyband is very large. In this case, since the CP length is shortened ininverse proportion to the subcarrier spacing, the basic unit (T_(TA)) ofthe TA value may be configured according to the subcarrier spacing ofthe SS block. In this case, T_(TA) may be determined in inverseproportion to the subcarrier spacing of the SS block, or may bedetermined on the basis of the rule predefined according to thesubcarrier spacing of the SS block. If necessary, T_(TA) may also bedetermined to be an arbitrary value according to one embodiment.

For example, assuming that the subcarrier spacing of the SS block is setto 15 kHz, T_(s) may be 1/30.72 MHz, and T_(TA) may be 4 Ts. Inaddition, assuming that the subcarrier spacing of the SS block is 120kHz, T_(s) may be 1/(8×30.72 MHz), and T_(TA) may be 4 T_(s). In theabove-mentioned examples, assuming that T_(s) is set to a fixed value,the value of N for use in ‘T_(TA)=N×T_(s)’ may be scaled on the basis ofthe T_(s) value. That is, assuming that T_(s) value is fixed to‘1/(16×30.72 MHz)’, when the subcarrier spacing of the SS block is 15kHz, T_(TA) may be 32 T_(s), and when the subcarrier spacing of the SSblock is 120 kHz, T_(TA) may be 4 T_(s).

2. Method 2: Method for Configuring Basic Unit of TA Value According toFrequency Band

According to a detailed method proposed in Method 1, it is assumed thatsubcarrier spacing of all channels is very large according to carrierfrequencies managed and operated by a base station (BS), such that theSS block is defined as a representative channel of all channels.However, according to the latest research and discussion known to thoseskilled in the art, the NR system may have a minimum system bandwidth of5 MHz within the range of 6 GHz or less, and may have a minimum systembandwidth of 50 MHz within the range of 6 GHz or higher.

If the subcarrier spacing of the SS block (i.e., the SS block subcarrierspacing) is set to 15 kHz, this means that a frequency band of the SSblock corresponds to about 4 MHz. Therefore, although the subcarrierspacing of the SS block for use in the frequency band of 3˜6 GHz is setto 15 kHz, the subcarrier spacing of a data channel may be 30 kHz or 60kHz. In addition, as the subcarrier spacing increases, the CP length isreduced. As a result, when T_(TA) is defined on the basis of thesubcarrier spacing (SCS) of the SS block in which the subcarrier spacingSCS is small, resolution of the TA value may be extremely decreased.Therefore, it may be more desirable that the basic unit of the TA valueis configured according to the frequency band. In this case, thefrequency band may refer to a carrier frequency band, and may also referto a frequency band number defined in the communication standard.

The following Table 2 exemplarily illustrates subcarrier spacing of theSS block, T_(s) values, and T_(TA) values according to respectivefrequency bands.

TABLE 2 Subcarrier spacing of Frequency band SS block T_(S) T_(TA) 300MHz~3 GHz    15 kHz 1/30.72 MHz 4T_(S) 3 GHz~6 GHz  15 kHz 1/(2 × 30.72MHz) 4T_(S) 6 GHz~40 GHz 120 kHz  1/(8 × 30.72 MHz) 4T_(S) 40 GHz~100GHz 120 kHz  1/(16 × 30.72 MHz)  4T_(S)

Referring to Table 2, as the frequency band increases, the T_(TA) valuedecreases. Although the same SS block subcarrier spacing is used, theT_(TA) value may be a smaller value at a higher frequency band. Inaddition, if T_(s) shown in Table 2 is defined as a fixed value, the Nvalue for use in ‘T_(TA)=N×T_(s)’ may be scaled according to the T_(s)value for convenience of description. In other words, assuming that theT_(s) value is fixed to ‘1/(16×30.72 MHz)’, T_(TA) shown in Table 2 maybe sequentially changed to 64 T_(s), 32 T_(s), 8 T_(s), and 4 T_(s) inthe top-to-bottom direction of Table 2.

3. Method 3: Method for Configuring Basic Unit of TA Value According toRACH Numerologies

In the LTE or NR system, the UE may initially attempt to perform ULtransmission through the RACH preamble during the initial access. Inthis case, the TA value may be set to zero ‘0’. ‘TA=0’ may indicate thatthe UE transmits the UL signal on the basis of a Rx time of a downlink(DL) signal. In this case, the BS may calculate an arrival time of theRACH preamble signal transmitted from the UE, and may transmit the TAvalue configured based on the arrival time of the RACH preamble signalto the UE through the RAR message. That is, resolution of the TA valuetransmitted through the RAR message may be determined by the bandwidthof the RACH preamble signal, and the bandwidth of the RACH preamblesignal may be proportional to the subcarrier spacing of the RACHpreamble. Therefore, the resolution of the TA value transmitted throughthe RAR message may be used as T_(TA) corresponding to the basic unit ofthe TA value that is transmitted through the TA command and is usedduring UL signal transmission of the UE. T_(TA) may be determined ininverse proportion to the subcarrier spacing of the RACH preamble, ormay be determined on the basis of the rule predefined according to thesubcarrier spacing of the RACH preamble. Alternatively, T_(TA) may alsobe set to an arbitrary value according to one embodiment.

The following Table 3 illustrates examples of T_(TA) determinedaccording to the subcarrier spacing of the RACH preamble.

TABLE 3 Subcarrier spacing of RACH preamble (Subcarrier spacing of RACHmsg1) T_(S) T_(TA) 15 kHz 1/30.72 MHz 8T_(S) 30 kHz 1/(2 × 30.72 MHz)8T_(S) 60 kHz 1/(8 × 30.72 MHz) 8T_(S) 120 kHz  1/(16 × 30.72 MHz) 8T_(S)

Referring to Table 3, T_(TA) may be determined in inverse proportion tothe subcarrier spacing of the RACH preamble. In addition, if T_(s) shownin Table 3 is defined as a fixed value, the N value for use in‘T_(TA)=N×T_(s)’ may be scaled according to T_(s) for convenience ofdescription. For example, assuming that the T_(s) value is fixed to‘1/491.52 MHz’, T_(TA) shown in Table 3 may be sequentially changed to128 T_(s), 64 T_(s), 32 T_(s), 16 T_(s) in the top-to-bottom directionof Table 3.

4. Method 4: Method for Configuring Basic Unit of TA Value According toDefault Numerology of Data Channel

As described above, the NR system may support various numerologieswithin a single system. For example, the NR system may simultaneouslysupport data channels (e.g., PDSCH, PUSCH, etc.) having differentsubcarrier spacings of 15 kHz˜60 kHz within the single system. However,although the NR system simultaneously supports data channels havingdifferent subcarrier spacings, the subcarrier spacing of some channels(e.g., SS block, RACH, etc.) used before a common signal commonly usedin UEs or UE-to-UE connection is established may be unavoidably fixed toonly one value. In this case, assuming that numerology of a signal suchas SS block or RACH is used as a reference channel or a referencesignal, the TA resolution may be extremely deteriorated or increased. Inthis case, the reference channel or the reference signal may refer to achannel or signal to be used for TA measurement.

According to the latest research or discussion, default numerology ofthe data channel is not yet defined in the NR system. However, assumingthat the default numerology of the data channel is defined, the defaultnumerology of the data channel may be used as a reference value fordeciding the T_(TA) value. This means that the T_(TA) value can bedetermined according to the default numerology of the data channel.Alternatively, according to the concept similar to the defaultnumerology of the data channel, numerology of a PDSCH used to transmit abroadcast channel (e.g., Remaining Minimum System Information (RMSI),Other System Information (OSI), or paging) or numerology of a PUSCH usedto transmit a RACH message3 (RACH msg3) may also be used as a referencevalue for deciding the T_(TA) value. Assuming that PDSCH numerology orPUSCH numerology is used as a reference value for deciding the T_(TA)value, this means that the T_(TA) value may also be configured accordingto PDSCH numerology or PUSCH numerology as necessary. In this case, theT_(TA) value may be determined in proportion to the subcarrier spacingof the default numerology of the data channel, or may be determined onthe basis of the rule predefined according to the subcarrier spacing ofthe default numerology of the data channel. Alternatively, the T_(TA)value may also be set to an arbitrary value according to one embodimentas necessary.

The following Table 4 illustrates exemplary T_(TA) values configuredaccording to RMSI numerology.

TABLE 4 Subcarrier spacing of RMSI T_(S) T_(TA) 15 kHz 1/30.72 MHz4T_(S) 30 kHz 1/(2 × 30.72 MHz) 4T_(S) 60 kHz 1/(8 × 30.72 MHz) 4T_(S)120 kHz  1/(16 × 30.72 MHz)  4T_(S)

Referring to Table 4, as an example of the broadcast channel, T_(TA) maybe set to different values according to the RMSI subcarrier spacing, andT_(TA) may be determined in inverse proportion to the RMSI subcarrierspacing. In addition, if T_(s) shown in Table 4 is defined as a fixedvalue, the N value for use in ‘T_(TA)=N×T_(s)’ may be scaled accordingto T_(s) for convenience of description. For example, assuming that theTs value is fixed to ‘1/491.52 MHz’, T_(TA) shown in Table 4 may besequentially changed to 64 T_(s), 32 T_(s), 16 T_(s), 8 T_(s) in thetop-to-bottom direction of Table 4.

5. Method 5: Method for Configuring Basic Unit of TA Value ThroughSystem Information

As described above, the NR system may simultaneously support datachannels having different subcarrier spacings of 15 kHz-60 kHz withinthe single system. In this case, the subcarrier spacing of some channels(e.g., SS block, RACH, etc.) used before a common signal commonly usedin UEs or UE-to-UE connection may not represent a preferred subcarrierspacing desired by a connected BS. In this case, the BS may directlyconfigure the T_(TA) value through system information. In addition, theBS may configure a preferred SCS or a supported maximum SCS, and mayalso configure the T_(TA) value according to the preferred SCS or thesupported maximum SCS. If the UE is assigned a plurality of carriers ora plurality of bandwidth parts, the UE may receive system informationfor each carrier or system information for each bandwidth part through aUE-specific message, such that the T_(TA) value may be configured percarrier or per bandwidth part.

6. Method 6: Method for Configuring Basic Unit of TA Value According toNumerology of Data Channel Configured Per UE or According to Numerologyof Reference Channel for TA Measurement

The above-mentioned methods 1˜5 have assumed that a basic unit of the TAvalue based on the RAR message is identical to a basic unit of the TAvalue of the TA command received in a connected mode. Therefore, theconcepts of Methods 1˜5 have been designed in a manner that T_(TA) isconfigured on the assumption that all UEs use the same subcarrierspacing. In Methods 1˜5, if all UEs do not use the same subcarrierspacing, the T_(TA) value may be determined based on a maximumsubcarrier spacing currently supported by the BS so as to implementefficient timing alignment.

Assuming that the basic unit of the TA value based on the RAR message isidentical to the basic unit of the TA value of the TA command receivedin the connected mode, the TA resolution may be deteriorated accordingto UEs, or it is necessary for the number of bits for transmitting theTA value to be increased to support the maximum subcarrier spacing.

In order to address the above-mentioned issues, Method 6 provides amethod for configuring the basic unit of the TA value according tonumerology of a data channel configured per UE or according tonumerology of a reference channel for TA measurement. In addition,Method 6 may include a method for allowing the basic unit of the TAvalue received through the RAR message to be different from the basicunit of the TA value received through the TA command in the connectedmode.

For example, if the UE is in an idle mode (i.e., before the UE finishesconnection setup), T_(TA) may be configured using Methods 1˜5.

However, if the UE is in the connected mode (i.e., after the UE finishesthe connection setup), the UE may configure the SCS of the data channel(e.g., PDSCH or PUSCH) or the SCS of the reference channel (e.g., SRS)for TA measurement, and may determine the T_(TA) value on the basis ofthe SCS of the data channel or the SCS of the reference channel for TAmeasurement. In addition, if DL subcarrier spacing is difference from ULsubcarrier spacing, T_(TA) may be determined based on the UL subcarrierspacing.

In addition, if the UE is allocated a plurality of carriers or aplurality of bandwidth parts and operates using the allocated carriersor bandwidth parts, subcarrier spacing of the data channel may beapplied in different ways according to the respective allocatedcarriers. In this case, it may be difficult for Methods 1, 3, 4 and 5 tobe equally used in all carriers, and it may be more preferable thatdifferent T_(TA) values are applied to individual carriers.(Hereinafter, the term “carrier” may refer to a bandwidth part used inone carrier for convenience of description) In this case, T_(TA) may bedecided based on the SCS of the allocated data channel, or may bedirectly decided through a connection setup message. Alternatively,according to one embodiment, the T_(TA) value configured before theconnection setup process may also be successively used as necessary.

In Methods 1˜5, the TA value may have the same TA resolution about asingle frequency band. Therefore, when the UE stores the TA valuereceived through the RAR message in a memory and then receives the otherTA value decided as a relative value in the connected mode, the UE mayuse the addition or subtraction operation using the TA value stored inthe memory without using the scaling process.

In contrast, in Method 6, the UE must adjust the TA value configuredthrough the RACH procedure according to the subcarrier spacing (SCS) ofthe data channel, and must then use the adjusted TA value. Therefore, ifthe UE stores the TA value received through the RAR message and the SCSof the data channel is decided, the UE may shift the TA value stored inthe memory by a predetermined value corresponding to the ratio of theSCS. In this case, 1-bit resolution about the memory may be T_(TA)corresponding to the RAR message.

In accordance with another embodiment, the UE may determine the bitresolution of the memory according to either a frequency band or amaximum SCS supported by the system. According to the bit resolution ofthe memory, the UE may perform scaling of the TA value received throughthe RAR message or the TA value received through the TA command in theconnected mode, and may then store the scaled TA value in the memory.

Method for Deciding Basic Unit of TA Value for Use in System OperatingThrough a Plurality of Frequency Bands

How to apply the above-mentioned method for configuring the basic unitof the TA value to a communication system capable of providing servicesthrough a plurality of frequency bands will hereinafter be described indetail. For example, in the case of using the LTE system, acommunication system capable of providing services through a pluralityof frequency bands may include the concept of carrier aggregation. TheNR system may include the concept of carrier aggregation or the conceptof a plurality of bandwidth parts (i.e., multiple bandwidth parts). Thatis, under the condition that the UE is allocated a plurality offrequency bands and the respective frequency bands have differentreference channels for configuring the basic unit of the TA value, amethod for determining the basic unit of the TA value on the abovecondition will hereinafter be described in detail. In this case, it isassumed that the TA command is transmitted through only one frequencyband from among plural frequency bands allocated to the UE, all thefrequency bands will hereinafter be referred to as a TA group (TAG).

Although the basic unit of the TA value is the SCS of the data channelallocated to the UE or the SCS of the SRS for TA measurement forconvenience of description, sub carrier spacing values of all theaforementioned reference channels may also be applied to the presentdisclosure without departing from the scope or spirit of the presentdisclosure.

The basic unit of the TA value may be determined on the basis of the SCSof the frequency band (i.e., reference channel) transmitting the TAcommand from among a plurality of channels. If the UE receives the TAcommand, the TA value may be determined based on the received TAcommand. In this case, the TA value may be calculated as an absolutetime, or may also be calculated as a UE-adjusted value that is adjustedaccording to a basic unit (e.g., the number of samples) decided by theUE. The decided TA value may be applied to all frequency bands.

In order to facilitate TA measurement of the BS, if the UE transmits achannel such as SRS to the BS, the UE may assist the TA measurement ofthe BS by transmitting the SRS through the frequency band capable oftransmitting the TA command. However, the scope or spirit of the presentdisclosure is not limited thereto. In accordance with one embodiment,the BS may directly configure the frequency band needed for SRStransmission in response to BS load or accuracy of TA value measurement.

If the frequency band for configuring the basic unit of the TA valueoperates with a small subcarrier spacing (SCS) and the basic unit of theTA value is decided according to the small SCS, the basic unit of the TAvalue may be extremely increased. Therefore, in the frequency band inwhich the operating SCS is large and the slot length is short, the TA isused as a larger unit than the slot length, interference between symbolsmay occur.

In order to address the above-mentioned issues, the basic unit of the TAvalue may be determined based on the SCS of the frequency band in whichthe SCS of a reference channel is at the highest value, from amongseveral frequency bands allocated as a reference for deciding the basicunit of the TA value. Upon receiving the TA command, the UE may decidethe TA value on the basis of the received TA command, and may apply thedecided TA value to all the frequency bands. In this case, the referencechannel may include various channels or signals as described above.

For example, if several frequency bands are allocated to the UE, sincethe UE has already entered the connected mode, it is preferable thatPUSCH/PUCCH or SRS to which TA is applied be used as a referencechannel. Therefore, from among several frequency bands to which the ULchannel is allocated, a channel/signal in which the SCS of PUSCH/PUCCHor the SCS of SRS is at the highest value may be set to a referencechannel, and the SCS of the reference channel may be used as a referencevalue for determining the basic unit of the TA value. If the SCS of thereference channel is used as a reference value for determining the basicunit of the TA value, this means that the basic unit of the TA value canbe configured on the basis of the SCS of the reference channel.

In addition, in the case of using the frequency band in which no ULchannel is allocated, the basic unit of the TA value may be configuredon the basis of the SCS of the PDSCH/PDCCH channels. In the case ofusing the frequency band in which the UL channel is allocated, the basicunit of the TA value may be configured on the basis of the highest valuefrom among subcarrier spacings (SCSs) of PUSCH/PUCCH or SRS.

Alternatively, in the frequency band in which no UL channel isallocated, the basic unit of the TA value may also be configured inconsideration of the possibility of UL channel allocation in asubsequent process as necessary. For example, in association with thefrequency band in which no UL channel is allocated, the basic unit ofthe TA value may be configured on the basis of the SCS of a givenchannel shown in Methods 1 to 4. In association with the frequency bandin which the UL channel is allocated, the highest value from among SCSvalues of PUSCH/PUCCH or SRS may be configured as the basic unit of theTA value.

Alternatively, even when no UL channel is allocated, in consideration ofthe possibility of UL channel allocation in a subsequent process, thebasic unit of the TA value about all the configured frequency bands maybe configured on the basis of the highest value from among SCS values ofa given channel shown in Methods 1 to 4.

In order to facilitate TA measurement of the BS, if the UE transmits achannel such as SRS to the BS, it may be preferable that the UEtransmits the SRS through a frequency channel determined to be thereference channel. However, according to one embodiment, the samechannels having the same SCS may be present, and the BS may directlyconfigure the frequency band for SRS transmission in consideration of BSload or accuracy of TA measurement.

FIG. 7 is a conceptual diagram illustrating exemplary methods forapplying a round-off or round-up operation to the TA value that iscalculated on the basis of the number of samples.

If different sampling frequencies operate in the respective frequencybands, and if the UE calculates the TA value received from the TAcommand on the basis of the number of samples and applies the calculatedTA value, the UE may perform scaling of the TA value received from theTA command according to each sampling frequency, may perform conversionof the scaled TA value on the basis of the number of samples, and mayuse the conversion resultant value. In this case, if the conversionresultant value based on the number of samples does not correspond to aninteger number about the sampling time, the UE may use the nearestinteger number. In this case, the UE may use a round-off or round-upoperation as necessary so as to use the nearest integer number. Forexample, as shown in FIG. 7, assuming that the basic unit of the TAvalue may be set to 16 T_(s) and the TA value received by the UE throughthe TA command is 4 T_(s), the UE may apply the TA value obtained by theround-off operation. In this case, since 4 T_(s) is less than 8 T_(s)corresponding to ½ of 16 T_(s), the applied TA value may be zero ‘0’.Therefore, the UE may transmit the UL signal without adjusting the UL Txtime point. If the TA value received by the UE through the TA command is10 T_(s), 10 T_(s) is higher than 8 T_(s) corresponding to ½ of 16T_(s), such that 16 T_(s) may be used as the TA value using the round-upoperation, and the UE may adjust a UL Tx time point by 16 T_(s) and thentransmit the UL signal at the adjusted Tx time point.

In accordance with another embodiment, the round-up or round-downoperation may also be applied to such TA calculation. For example,assuming that the basic unit of the TA value is set to 16 T_(s) and theTA value is calculated using the round-up operation, when the TA valuereceived by the UE through the TA command is set to 4 T_(s) or 10 T_(s),16 T_(s) may be used as the TA value according to the round-upoperation.

In contrast, assuming that the TA value is changed to an absolute valueand the resultant absolute value is used, the UE may apply different TAvalues to individual frequency bands using the absolute value that hasbeen changed based on an operation unit for each frequency band.

Considerations of UE Operation about Concatenated Mini-Slots

In the meantime, in order to improve (or increase) a data reception (Rx)region during the data Tx/Rx process of a communication system, a methodfor performing packet transmission in a manner that a packet isconcatenated with a plurality of slots may be used in the communicationsystem. In this case, within each slot, a reference signal (S) forchannel estimation may be transmitted to demodulate or recover data froma received signal, the UE may perform channel estimation using the RSand may receive signals using the RS. In this case, if a transmitter(e.g., UE) performs time tracking or abruptly changes a currentfrequency to another frequency at an intermediate position of theconcatenated slots, characteristics of a channel corresponding to eachslot may be changed from the viewpoint of a receiver (e.g., BS).Therefore, considering the above-mentioned case, the channel estimatedin each slot is generally applied only to the estimated slot withoutbeing applied to a subsequent or previous slot.

If a request for packet transmission occurs in the LTE or NR system, theLTE or NR system aims to define a mini-slot in which the data channelfor data transmission has a short slot so as to reduce a time delayneeded for data transmission, as well as to provide a low latencyservice using the mini-slot. Since the mini-slot has a short slotlength, spacing in time between slots is small. However, if RS istransmitted per slot, the ratio of overhead may extremely increase. As aresult, when data transmission is performed using concatenated slots,many developers and companies are conducting intensive research intovarious methods for allowing the RS having been used in one slot to besuccessively used in the subsequent or previous slot, withouttransmitting the RS for each slot.

As described above, assuming that the RS is shared by several slots, ifthe transmitter performs time tracking at a boundary position ofconcatenated slots, the receiver does not recognize such time trackingof the transmitter, performs channel estimation at the slot in which theRS has been transmitted, and applies the channel estimation result tocontiguous slots, such that the data Rx performance may be greatlydeteriorated. In order to address the above-mentioned issues, thepresent disclosure provides a method for allowing the UE to receive theTA command as well as to apply a TA value received through the TAcommand, and a detailed description thereof is as follows.

First, if the UE is allocated concatenated mini-slots by sharing the RSin the process for receiving the TA command and applying the TA valuereceived through the TA command to the transmitter of the UE, the UE maynot apply the TA value to transmission of concentrated mini-slots so asto decide a Tx time point of the transmitter. The UE may use the TAvalue as a parameter of the transmitter, after transmission completionof concatenated mini-slots. In addition, although a time at whichapplication of the TA value is started is predefined, the UE may delaythe TA value and may use the delayed TA value. Therefore, the UE canreceive a transmission (Tx) packet without any problems.

Second, the BS having transmitted the TA command and the UE configuredto receive the TA command and apply the TA value to the received TAcommand may predefine a TA application time at which the TA value willbe applied. If transmission of the concatenated mini-slots is attempted,accurate application of the TA value is possible. Therefore, the BS mayaccurately apply the TA value to the channel estimation value, such thatthe resultant value can be applied to the data reception process. Inthis case, a specific time at which the TA value will be applied formini-slot transmission may be defined in units of a slot or symbol(e.g., OFDM symbol for use in the OFDM symbol) used to define themini-slot.

Alternatively, in order to prevent the UE operation from beingcomplicated, the TA application time may be defined on a basis of a unitlarger than the slot unit of the mini-slot. In addition, a restrictionmethod for allowing the BS (transmitting the TA command) to schedule theconcatenated mini-slots while simultaneously avoiding the TA applicationtime may also be used. If necessary, the above-mentioned method may notbe applied to other concatenated mini-slots not sharing the RS.

As described above, a delay time occurs in the application process ofthe TA command, and additional TA commands are received during thesection having such delay time, such that the accumulated TA value to befinally used may be extremely increased. In this case, if theaccumulated TA value is applied at once, the receiver of the BS mayreceive time tracking information or may have an unexpected problem indata reception. In order to prevent occurrence of such problem, theaccumulated TA value may be divisionally applied to a plurality ofpoints. In this case, a reference of classifying the plurality of pointsmay be decided on the basis of pre-configured upper/lower limit valuesor other upper/lower limit values applied by the BS. In addition, the UEmay be arbitrarily applied on the basis of the accumulated TA value,without being applied to individual TA values received through therespective TA commands.

FIG. 8 is a flowchart illustrating a method for allowing the UE totransmit the uplink (UL) according to an embodiment of the presentdisclosure.

Referring to FIG. 8, the UE may receive a random access response (RAR)message including the first TA command in step S800.

In step S810, the UE may determine a first TA value for transmitting afirst UL signal on the basis of not only the subcarrier spacing of theUL channel to be initially transmitted after reception of the RARmessage, but also the first TA command.

For example, the basic unit of the TA value may be determined on thebasis of the subcarrier spacing of the UL channel to be initiallytransmitted after reception of the RAR message. In this case, thesubcarrier spacing of the RACH msg3 may be recognized by the UE throughRACH configuration. The first TA value may be determined on the basis ofthe basic unit of the TA value and the first TA command. When the UEtransmits the UL signal through a single UL carrier, the first TAcommand may refer to a TA command to be received by the UE through RARduring the idle mode or the connected mode of the UE. In addition, thefirst TA command may also refer to the TA command received through a MACCE during the connected mode of the UE. In this case, the first TA valuemay be in proportion to the value indicated by the first TA command, andmay be in inverse proportion to the subcarrier spacing of the UL channelto be initially transmitted after reception of the RAR message.

The UL channel to be initially transmitted after reception of the RARmessage may refer to ‘RACH msg3’ when the UE is in the idle mode, andmay refer to a PUSCH when the UE is in the connected mode.

In step S820, the UE may transmit a first UL signal according to thefirst TA value. In this case, a first UL signal to be transmittedaccording to the first TA value may include the UL channel to beinitially transmitted after reception of the RAR message. For example,the UE in the idle mode may transmit ‘RACH msg3’ according to the firstTA value.

FIG. 9 is a diagram illustrating a configuration of a user equipment(UE) and a base station (BS).

The UE 100 according to the present disclosure may include a transceiver110, a processor 120, and a memory 130. The transceiver 110 of the UE100 may be referred to as a radio frequency (RF) unit or a Tx/Rx module.The transceiver 110 may be configured to transmit and receive varioussignals, data and information to and from an external device.Alternatively, the transceiver 110 may be divided into a transmitter anda receiver. The UE 100 may be connected to the external device by wireand/or wirelessly. The processor 120 may control overall operation ofthe UE 100, and be configured to calculate and process information forthe UE 100 to transmit and receive to and from the external device. Inaddition, the processor 120 may be configured to perform the proposedoperations of the UE 100. The processor 120 may also be configured tocontrol the transceiver 110 to transmit data or messages according tothe proposal of the present disclosure. The memory 130 may store thecalculated and processed information for a predetermined time, and maybe replaced by another constituent such as a buffer (not shown).

Referring to FIG. 9, the BS 200 according to the present disclosure mayinclude a transceiver 210, a processor 220, and a memory 230. If the BS200 communicates with the UE 100, the transceiver 210 may be referred toas a Tx/Rx module or a radio frequency (RF) unit. The transceiver 210may be configured to transmit and receive various signals, data andinformation to and from an external device. The BS 200 may be connectedto the external device by wire and/or wirelessly. The transceiver 210may also be divided into a transmitter and a receiver. The processor 220may control overall operation of the BS 200, and be configured tocalculate and process information for the BS 200 to transmit and receiveto and from the external device. In addition, the processor 220 may beconfigured to perform the proposed operations of the BS 200. Theprocessor 220 may also be configured to control the transceiver 210 totransmit data or messages according to the proposal of the presentdisclosure. The memory 230 may store the calculated and processedinformation for a predetermined time, and may be replaced by anotherconstituent such as a buffer (not shown). The BS 200 may be eNB or gNB.

For configuration of the UE 100 and the BS 200, the details described invarious embodiments of the present disclosure may be independentlyapplied or implemented such that two or more embodiments aresimultaneously applied. For simplicity, redundant description isomitted.

The processor 120 of the UE 100 according to the present disclosure maycontrol the transceiver 110 to receive the RAR message including thefirst TA command, and may determine the first TA value for transmittingthe UL signal based on the first TA command and the subcarrier spacingof the UL channel to be initially transmitted after reception of the RARmessage. As described above, when the UE transmits the UL signal throughone UL carrier, the first TA command may refer to a TA command to bereceived through RAR during the idle mode or connected mode of the UE.In this case, the UL channel to be initially transmitted after receptionof the RAR message may refer to ‘RACH msg3’ when the UE is in the idlemode, and may refer to a PUSCH when the UE is in the connected mode. Forexample, if the UE is in the idle mode, the UE may receive the first TAcommand through the RAR message, and the first TA value may bedetermined on the basis of the value indicated by the first TA commandand the basic unit of the TA value. In this case, the basic unit of theTA value may be determined based on the subcarrier spacing of ‘RACHmsg3’.

When the UE is in the connected mode, the UE may receive the first TAcommand through the RAR message or the MAC CE. In this case, the firstTA command transmitted through the MAC CE may refer to a TA command thatis periodically transmitted, and may indicate an updated value about theprevious TA value. In this case, the first TA value may be determinedbased on the basic unit of the TA value and the value indicated by thefirst TA command. When the UE is in the connected mode, the basic unitof the TA value may be determined based on the subcarrier spacing of aPUSCH to be initially transmitted after completion of RAR. In addition,when the UE receives the first TA command through the MAC CE, the firstTA value may be determined by applying the value indicated by the firstTA command to the previous TA value.

The UE may control the transceiver 110 to transmit the first UL signalaccording to the first TA value. In this case, the first UL signal to betransmitted according to the first TA value may include the UL channelto be initially transmitted after reception of the RAR message. Forexample, the UE in the idle mode may transmit ‘RACH msg3’ according tothe first TA value.

In addition, if the UE is allocated a plurality of UL bandwidth parts,the basic unit of the TA value may be determined based on largest valueamong subcarrier spacing values of the plurality of UL bandwidth parts.For example, the UE may receive a DL channel including a second TAcommand. In this case, the second TA command may refer to a TA commandto be transmitted from the BS when the UE has the plurality of ULbandwidth parts. The UE may determine the second TA value fortransmitting the second UL signal based on the second TA command. Forexample, the second TA value may be determined based on the basic unitof the TA value and the value indicated by the second TA command. If theUE is allocated a plurality of UL bandwidth parts, the basic unit of theTA value may be set to the largest SCS value among SCS values of PUSCH,PUCCH, or SRS in the plurality of UL frequency bands.

In addition, when the UL signal is transmitted in an uplink (UL)bandwidth part, that has a smaller SCS than the SCS used to configurethe basic unit of the TA value, among the plurality of UL bandwidthparts, the second TA value may be determined by rounding-offTA-associated information based on the basic unit of the TA value.

The embodiments of the present disclosure may be implemented throughvarious means. For example, the embodiments may be implemented byhardware, firmware, software, or a combination thereof.

When implemented by hardware, a method according to embodiments of thepresent disclosure may be embodied as one or more application specificintegrated circuits (ASICs), one or more digital signal processors(DSPs), one or more digital signal processing devices (DSPDs), one ormore programmable logic devices (PLDs), one or more field programmablegate arrays (FPGAs), a processor, a controller, a microcontroller, amicroprocessor, etc.

When implemented by firmware or software, a method according toembodiments of the present disclosure may be embodied as an apparatus, aprocedure, or a function that performs the functions or operationsdescribed above. Software code may be stored in a memory unit andexecuted by a processor. The memory unit is located at the interior orexterior of the processor and may transmit and receive data to and fromthe processor via various known means.

As described before, a detailed description has been given of preferredembodiments of the present disclosure so that those skilled in the artmay implement and perform the present disclosure. While reference hasbeen made above to the preferred embodiments of the present disclosure,those skilled in the art will understand that various modifications andalterations may be made to the present disclosure within the scope ofthe present disclosure. For example, those skilled in the art may usethe components described in the foregoing embodiments in combination.The above embodiments are therefore to be construed in all aspects asillustrative and not restrictive. The scope of the disclosure should bedetermined by the appended claims and their legal equivalents, not bythe above description, and all changes coming within the meaning andequivalency range of the appended claims are intended to be embracedtherein.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable not only to 3GPP systems, but alsoto various wireless communication systems including IEEE 802.16x and802.11x systems. Moreover, the proposed method can also be applied tommWave communication using an ultra-high frequency band.

1. A method of transmitting uplinks signal by a user equipment (UE) in a wireless communication system, the method comprising: receiving a random access response (RAR) message including a first timing advance (TA) command; determining a first timing advance (TA) value for transmitting a first uplink signal, based on the first TA command and a subcarrier spacing of an uplink channel transmitted first after reception of the RAR message; transmitting the first uplink signal based on the first TA value; receiving a downlink channel including a second TA command; determining a second TA value for transmitting a second uplink signal, based on the second TA command; and transmitting the second uplink signal based on the second TA value, wherein, when the UE has a plurality of uplink bandwidth parts, the second TA value is determined based on the second TA command and a maximum value among subcarrier spacing values of the plurality of uplink bandwidth parts.
 2. The method of claim 1, wherein a basic unit of a TA value is determined based on the subcarrier spacing of the uplink channel transmitted first after reception of the RAR message, wherein the first TA value is determined based on the basic unit of the TA value and the first TA command.
 3. The method of claim 1, wherein the first TA value is in proportion to a value indicated by the first TA command, and is in inverse proportion to the subcarrier spacing of the uplink channel transmitted first after reception of the RAR message.
 4. (canceled)
 5. The method of claim 1, wherein: when the second uplink signal is transmitted in an uplink bandwidth part having a subcarrier spacing smaller than a subcarrier spacing used for determining the second TA value among the plurality of uplink bandwidth parts, the second TA value is determined by rounding-off a value indicated by the second TA command based on a basic unit of a TA value.
 6. A user equipment (UE) for transmitting uplink signals in a wireless communication system, the UE comprising: a transceiver; and a processor, wherein the processor configured to: control the transceiver to receive a random access response (RAR) message including a first timing advance (TA) command; determine a first timing advance (TA) value for transmitting a first uplink signal, based on the first TA command and a subcarrier spacing of an uplink channel transmitted first after reception of the RAR message; control the transceiver to transmit the first uplink signal based on the first TA value, control the transceiver to receive a downlink channel including a second TA command; determine a second TA value for transmitting a second uplink signal, based on the second TA command; and control the transceiver to transmit the second uplink signal based on the second TA value, wherein, when the UE has a plurality of uplink bandwidth parts, the second TA value is determined based on the second TA command and a maximum value among subcarrier spacing values of the plurality of uplink bandwidth parts.
 7. The UE of claim 6, wherein a basic unit of a TA value is determined based on the subcarrier spacing of the uplink channel transmitted first after reception of the RAR message, and wherein the first TA value is determined based on the basic unit of the TA value and the first TA command.
 8. The UE of to claim 6, wherein the first TA value is in proportion to a value indicated by the first TA command, and is in inverse proportion to the subcarrier spacing of the uplink channel transmitted first after reception of the RAR message.
 9. (canceled)
 10. The UE of to claim 6, wherein: when the uplink signal is transmitted in an uplink bandwidth part having a subcarrier spacing smaller than a subcarrier spacing used for determining the second TA value among the plurality of uplink bandwidth parts, the second TA value is determined by rounding-off a value indicated by the second TA command based on a basic unit of a TA value. 